1. Field of the Invention
The present invention relates to an oil pump which is an internal contact gear pump, wherein each inter-tooth space formed by an inner rotor and an outer rotor transports a fluid from an intake port to a discharge port while minimizing and smoothing the change in pressure of the fluid enclosed in the inter-tooth space and preventing eroding of the inside of the pump due to cavitation and erosion, while having an extremely simple construction.
2. Description of the Related Art
There many types of pumps with inter-tooth chambers formed by an inner rotor and outer rotor equipped with trochoidal teeth, which discharge a fluid from a discharge port by moving the inter-tooth chamber filled with fluid from an intake port with a maximum volume condition to a reduced volume stroke. With these pumps, when the inter-tooth chamber carries fluid from an intake port to a discharge port, the volume of the inter-tooth chamber, which has a trochoidal tooth structure, will gradually change. In other words, the volume of the inter-tooth space will increase and decrease while moving from the intake port to the discharge port, so the pressure of the fluid in the inter-tooth chamber will vary.
Furthermore, when the inter-tooth chamber reaches the discharge port, the fluid enclosed at high pressure in the inter-tooth chamber will abruptly enter the discharge port, causing loud and unusual noises. In order to prevent the fluid from abruptly flowing into the discharge port in this manner, a pump with a small port formed on the discharge port side has been disclosed in U.S. Pat. No. 2,842,450. This small port is a shallow groove formed from the leading edge of the discharge port to the intake port side.
Therefore, a small amount of the high-pressure fluid in the inter-tooth chamber will be discharged into the discharge port through the small port before the inter-tooth chamber reaches the discharge port, because the inter-tooth chamber intersects with the small port and communicates with the discharge port through the small port. Therefore when the inter-tooth chamber reaches the discharge port, the fluid in the inter-tooth chamber will not abruptly flow into the discharge port, and pump noise can be prevented.
According to the referenced patent (U.S. Pat. No. 2,842,450), the high-pressure fluid in the inter-tooth chamber which moves from the intake port to the discharge port is prevented from abruptly flowing into the discharge port and the generation of large noise can be prevented. However, as described above, the inter-tooth chamber increases and decreases in volume during the process of moving the fluid from the intake port to the discharge port, and the pressure of the fluid enclosed inside will vary. This change in fluid pressure causes cavitation where vapor bubbles are formed in the fluid. The vapor bubbles created by cavitation will congregate on the gear bottom side on the inner rotor side of the inter-tooth chamber.
Furthermore, the small port disclosed in the referenced patent (U.S. Pat. No. 2,842,450) will directly intersect with the inter-tooth chamber which moves toward the discharge port side, and at the moment when communicated with the inter-tooth chamber, pressure variation will occur at the small port, and there is a possibility that the vapor bubbles collected at the gear bottom parts of the inner rotor will abruptly collapse (destruct). At this time, the small port will not be able to accommodate the change in hydraulic pressure, and there is a possibility of erosion where the vapor bubbles caused by cavitation will abruptly collapse (destruct).
Because of this erosion phenomenon, the momentary generation and collapse (destruct) of a plurality of vapor bubbles will cause impact scarring on the inner rotor, outer rotor, and housing or the like, the pump efficiency will be negatively affected, and maintaining a predetermined pump performance will be difficult. In other words, even though the fluid which is in the inter-tooth chamber which transports the fluid to the discharge port can be prevented from abruptly flowing into the discharge port, eroding cannot be prevented, and there is a possibility that erosion will occur.